Fault indicating system for control circuits



R. w. cnca-wmw FAULT INDICATING SYSTEM FOR CONTROL CIRCUITS Nam 27, 7/

Filed Sept. 29, 1948 3nventor Patented Nov. 27, 1951 t UNITED STATESPATENT OFFICE FAULT INDICATING SYSTEM FOR CONTROL CIRCUITS Russell W.Cochran, Aliquippa, Pa.; Emilienne Cochran, exccutrix of Russell W.Cochran, deceased, assignor to Emilienne Cochran, Aliquippa, Pa.

Application September 29, 1948, Serial No. 51,730

7 Claims. (Cl. 177-311) 1 2 This invention relates to electromagnetcontrol ciator or similar device are interposed in resystems, and moreparticularly to a means for spective loop circuits connectedrespectively indicating which of a plurality of protective conaround theseveral series-connected contacts of tacts has opened to effectdeenergization of an the protective devices. The annunciatorwindelectromagnetic control means for a translating 5 ings areresponsive to the voltage induced in device. the winding of thecontactor or relay upon open' This application is a continuation-in-partof ing of one or more of the series-connected conmy copendingapplication Serial No. 723,697, filed tacts, and means are providedwhich permit cur- January '23, 1947, now abandoned. rent to pass throughthe annunciator winding Many electromagnetic control systems require 1during the brief period of this induced voltage that a plurality ofprotective devices such as but which prevent the flow of current afterthe limit switches, overload relays, and the like have inductivedischarge surge has subsided. When their respective normally-closedcontacts conall of the contacts of the protective devices arenected inseries with each other and with the closed, o cu r t ws through theonmllloioperating winding of a contactor or relay conator windings- Wone f the Protective trolling the supply of voltage to the controlledtacts opens, the transient voltage induced in the device which may be,for example, an electric W of the contactor relay is added to motor. Thenormally-closed contacts of one or the line volta e and causes a surgecurrent to more of the protective devices open upon occurflow r h t onef the n n l r W rence of abnormal conditions to deenergize the insswhich is connected in parallel with h pr series-connected contactor orrelay. The prot ot v n c that p An immediate tective devices thus areoperative to disconnect H l in ic ti s th y r v to w which the motorfrom its source of supply when abof the several protective contacts hasoperated to normal conditions occur. Depending upo the cause theshut-down. Since the annunciator type of protective devices utilized,the abnorwindings are Connected in l p r i r n mal conditions may beeither in the motor itthe protective contacts, it is important that theself, the motor circuit, the mechanism driven parallel circuits thusformed be incapable of conby the motor, or in a related control system,ducting current of sufiicient magnitude and duran the ease of a motor,for example, the opertion to prevent drop out of the contactor or atingwinding of the main line contactor or the relay. Many irect current op rt d contactors operating winding of an under voltage relay 0r relaysremain closed even though the current might have connected in seriestherewith the in their opera in w n has re ed to ten respectivenormally-closed contacts of an overp t of s normal value he ssary loadrelay, various field protective relays, a speed reduction in currentflow is accomplished in acresponsive device, a plurality of l m t it hcordance with the present invention by connectand one or more relay theoperation of which ing in series with each of the annunciator windisdependent upon the operation of related coninss a d vi e capa f u tin urnt nly trollers. The large number of such normallyurin th n v l a h h re vol a closed protective contacts in a control system exists andthereafter capable of pr v ntin th maybe such as to render diflicult thedeterminai now of current through the loop circuit. For tion' of whichone has operated to cause a shutfurther safety, th l p ir uit includingthe down of the apparatus. This is because many of l d n ln i t r W ning is interrupted by the normally-closed protective contacts are ofContacts Which p upon energization of the the automatic reclosing typeso that after they n un ia r Win in have opened to shut down theapparatus they 4 Loop circuits for the operation of annunciators returnto their normal positions and leave no mpl y n lt rna in currentintroduce certain indication that they have operated.Furtherdifficulties due to the matching of impedances more, theprotective contacts may be spaced at which Would be q l O the otherhand, considerable distances from each other, for inif direct c r e t We e p y in such a D stance, at the top and bottom of a skip hoistannunciator circuit, a large volta e su would supplying a blast furnaceor at each floor of be available and would assure an adequate voltanelevator system. Consequently, fault locaa e increas so h m t hi f impan tors or indicators have been developed which are would becomeunnecessary, and in fact, due to capable of giving a visual or otherindication of he l w h l -in vol a e of direc current device which ofthe plurality of protective contacts has the matching of impedanceswould be impractical. opened to cause a shut-down of the protectedHowever, since the voltage surge requires direct device. v current andthe direct current devices in turn In accordance with this invention,there is prohave a low hold-in voltage, there is introduced vidcd animproved fault indicator in which the the danger of improper ,by-passing01' the proseveral operating windings of a suitable annunco tectivecontacts. In order to take advantage of ways present the danger that thecontacts may close its normally-open contactsla,

operate improperly or may fail to operate. In

order to render the installation completely safe, therefore, a condenseror other current limiting or interrupting means also should beinterposed in the loop circuit. The concurrent solution of all of thesecorrelated problems is therefore necessary to assure safety of operationunder all operating conditions":

It is an object of .this invention to provide an improved means forindicating which of a plurality of series-connected protective contactshas opened.

Another object is to provide a fault finder comprising an annunciatorhaving its several operating windings connected in parallel,respectively, with the series-connected normally-closed contacts of aplurality of protective devices.

A further object is to provide a fault finder of the foregoing typeusable on direct current systems. .A related object is to provide afault finder of theforegoing type in which the resistance of theannunciator winding need not be related to the drop-out or pick-upvoltage of the contactor or relay controlled by the protective contacts.

Still another object is to provide a fault finder comprising annunciatorelements which operate in response to the inductive discharge voltage ofan electromagnetic device when deenergized by opening of a protectivecontact.

Another object is to provide a-means in a circuit paralleling aprotective contact and including an annunciator winding which meanspositively prevents the parallel circuit from conducting current afterthe transient produced by deenergization of an associatedelectromagnetic device has subsided.

Further objects and advantages of this invention will become apparentfrom the. following description wherein reference is made to thedrawings in which: I

Fig. l is a schematic wiring diagram illustrating one embodiment of theinvention applied in f a control system for an A.-C. motor and utilizinga D.-C. source for the motor control circuits.

Fig. 2 is a schematic wiring diagram of a modification and illustrateshow the invention may be applied in a control system for a directcurrent motor.

Figs. 3.and 4 are fragmentary wiring diagrams of. further modifications,respectively; and

Fig. 5 is a schematic wiring diagram of an additional modificationapplied in the control of a nA.-C. motor utilizing an A.-C. source forthe motor control circuit.

Referring to Fig. l, the controlled translating device is shown as apolyphase synchronous motor II] having an'armature winding Ina and afield winding IOb whichis supplied from a suitable source of directcurrent. Alternating current is supplied to the armature winding Illafrom a suitable supply line I3 under the control of electromagneticcontactors I4'and I5. As will be explained hereinafter, the contactor I4is operatedtoclose itsnormally-open contacts I411, Mb, andI Ic to startthe fm'otor on reduced voltage taken from intermediate taps on,thewindingsof auto trahsformers I6. Other meanssuch as resisters orreactors may, be used if desired to obtain the reduced starting voltage.The contactor I5 is the running contactor and, after the motor hasaccelerated to a predetermined speed and the contactor I4 has opened, isoperated to I51), and I5c to continue the operation of the motor ID onthe full voltage of the supply line I3.

The contactors I4 and I5 are of well-known construction having operatingwindings NW and I5w, respectively. These windings are adapted to beenergized from a'suitable direct current supply line H. The circuits forwindings I4w and I5w illustrated in Fig. 1 have been reduced to bareessentials for clarity of explanation. It will be understood that thecircuits of an actual controller would include many other features notshown. In the. elementary control system shown in Fig. l, the windingI4w of the starting contactor I4 is controlled by a normally-openpushbutton I8. The circuit for the winding I4w also includesnormally-closed contacts I9 of a speedresponsive device 20 which servesto transfer the motor ID from starting to running voltage and also tointerlock the windings I41 and I5w to prevent simultaneous energizationthereof The winding I5w of the running contactor I5 has connected inseries therewith a plurality of normally-closed contacts 2I, 22, and 23of a plurality of protective devices. The contacts 2I, 22, and 23 may,for example, be the contacts of such protective devices, not shown, asan overload relay, a field-failure relay, and an over-speed mechanism.Whatever the nature of the protective devices controlling or includingthe normallyclosed contacts 2I, 22, and 23, their function is todeenergize the winding I5w of the running contactor I5 in order todisconnect the armature winding Illa from the supply line I3 uponoccurrence of one or more abnormal conditions. The circuit of thewinding I5w also includes normally-open contacts 24 of thespeed-responsive device 20 and a normally-closed push button 25.

The circuits so far described represent standard practice and form nopart of my invention. In the operation of the motor control system ofFig. 1, starting of the motor I0 is initiated by closing thepush buttonI8 to energize the winding I4w of the starting contactor. I4 from thedirect current supply line H. The contactor. I4 thereupon moves to itsoperated position and the motor In starts due to the impressiongof'areduced alternating voltage on its armature winding la and acceleratestoward a predetermined speed. The push button I8 must be held closeduntil the motor Ill has accelerated sufiiciently to permit full voltageto be applied. When the motor. I0 reaches the speed desired for voltagetransfer, the speed responsive device 20 operates to open its contactsI9 and to close its contacts 24. The winding I4w is thus deenergized toeffect opening the contacts I4a, I41), and Me. Concurrently, the windingI5w is energized and the contactor I5 closes its contacts I5a, I5b,

and I to apply full voltage to the motor IIl if all of the protectivecontacts 2|, 22, and 23 are closed. I f

Under normal conditions, the contacts 2I, 22, and 23 remain closed andthe motor continues in operation until the pushbutton 25 is opened.Opening of the push button 25 deenergizes the winding I510 and causesthe contactorI5 toopen its contacts thereby to'eifect deenergization ofthe motor Ill, The occurrence of abnormal, conditions in the motor It orequipment driven by it causes one or more of the protective contacts 2|,22, and 23 to open and similarly disconnects the motor from the sourceof supply.

In order to provide an immediate and readily observable indication as towhich of. the protective devices has operated to disconnect the motor IDfrom the supply line I3, a plurality of loop circuits 26, 27, and 28 areconnected around the normally-closed protective contacts 2|, 22, and 23,respectively. The loop circuits 2E, 21, and 28 include operatingwindings 29w, 3020, and 31w, respectively, of a suitable annunciatorwhich are connected in series, in the respective loop circuits, with aplurality of current blocking means such as condensers 32, 33, and 34,respectively. As will be explained hereinafter, the condensers preventthe flow of current through the loop circuits around their associatedprotective contacts to the winding w after the inductive dischargevoltage oi the winding 15w has subsided. The loop circuits and 21 have acommon portion including normally-closed contacts 29a, the loop circuits2! and 28 have a common portion including normally closed contacts a,and the loop circuit 28 is completed by normally-closed contacts 3la.

Preferably the annunciator is of rugged construction and is one in whichthe indicating means is retained in indicating position after itsassociated operating winding has been deenergized. As illustrated, theannunciator is of the drop type and the operating windings 2910, 3020,and 3lw are magnetically associated with suitable indicating mechanisms,respectively, comprising clapper-type magnetic armatures 29b, 30b, and3|?) which, when moved to their energized position, effect opening ofthe normallyclosed contacts 29a, 38a, and 31a, respectively. Since theseveral mechanisms are identical, a detailed description of only one issuflicient. The armature 29b is arranged to retain an indicating flagmember 290 in a normal non-indicating position as shown. The flag member290 is suspended from one end portion of a centrally-pivoted link 1 29dhaving its other end portion normally retained in a lower position bylatching engagement with the armature 2972. Upon energization of thewinding 29w, the armature 2% moves to its attracted position releasingthe link 29d and permitting the flag member 290 to drop to an observableindicating position. Concurrently, the contacts 29a are opened. Thecontacts 29c can be reclosed and the flag 29c raised to nonindicatingposition only by manually re-engaging the link 29d with the armature2912.

Upon opening of any one of the contacts 2|, 22, or 23, the currentdecreases and eventually ceases to flow through the winding l5w. As aresult of the relatively high inductance of the winding I5w, a largetransient voltage surge or inductive kick results from the collapsinglines of the magnetic force through the core of the winding cutting theturns of the latter. This transient voltage is added to the line voltageand causes a current impulse to flow through the loop circuit around theprotective contact that has opened. Normally the series connectedannunciator winding, the condenser, and the associated interlock contactin this loop circuit are by-passed by the respective contact 2%, 22, or23, and no voltage is impressed upon the winding in the loop. When theprotective contact opens, however, the associated loop circuit iseffectively connected in series with the winding l5w across the sourceH. The

voltage induced in the winding l'5w is much higher than the line voltageand causes a transient charging current to flow through the one of theloop circuits 25, 21, or 28 which is connected around the opened one ofthe protective contacts. This transient current causes the dropping ofthe proper one of the several flag members giving an immediate visibleindication as to which protective contact has opened. The flag membersare preferably coded as by numbering in accordance with similar numberson its associated protective contacts. With this immediate indication asto which protective contact has opened, no time is lost in determiningthe source of the fault which caused the motor I 6 to shut down. Allthat is required in order to restore the indicating system for furtheroperation is to reset the armature and link mechanism which operated toindicate the fault.

The operation of the control system of Fig. 1 will be explained morespecifically with the assumption that the protective contacts 21 haveopened. Opening of the contacts 2! causes the discharge voltage of thewinding lbw to be added to that of the line and the combined voltageforces a current through the loop circuit 26 including the seriesconnected condenser 32, the winding 2910, and the normally-closedcontacts 29a. This momentary surge of current is willcient to cause thearmature 29b to be moved to its attracted position by the winding 29w.When the armature 23b reaches its attracted position the link 29d isreleased and the flag 29c drops to an observable position. Concurrently,the contacts 29a open to interrupt the only remaining low impedancecircuit to the winding l5w. This impulse of current through the shuntcircuit also starts to charge the condenser 32 which, if the contacts29a had for any reason failed to open, would have reached a chargedcondition preventing the further flow of current to the winding i520.Consequently, it is seen that the protective contacts are by-passed byshunt circuits each of which includes two separate means to prevent thecontinued flow of current through the shunt circuit to the controlledwinding after one of the protective contacts has opened. Each of theother protective contacts and associated shunt circuits operates in asimilar manner as outlined above.

After the fault has been corrected and the protective contact whichopened has returned to its normal position, the motor It] may bereaccelerated by operation of the push button la in the same manner asdescribed hereinbefore.

Referring now to Fig. 2, a direct current motor 35 is arranged to beconnected for energization from a suitable supply line 39 through asuitable current-limiting acceleration and speed control means 3'! whena knife switch 38 and an electromagnetic contactor 39 are both in theirclosed positions. The motor 35 has an armature winding 35a and may havea series field winding 35b and a shunt field winding 350 the latter ofwhich i is supplied from a suitable source of direct current asindicated. The contactor 39 has an operating winding 39w and also hasnormally-open main contacts 33a. and 39b in series with the motorarmature 35a. A master switch 40 has stationary contacts 4! and 42adapted to be bridged by a contact segment 43 in its on position andstationary contacts 44 and 45 adapted to be bridged by the segment 43 inits operative or on position. The master switch s9 is arranged tocontrol the energization of an under voltage relay 46 having anoperating winding 46w and normally-open contacts 46a and in turncontrols the operation of the contactor 39. It will be understood thatthe master switch 4|! may have many more contacts and segments and beused to control also the acceleration and speed control means 31.Connected in series with each other and in series with the winding 4510are the plurality of normally-closed series connected protectivecontacts 2|, 22, and 23 of Fig. 1. When the master switch 40 is in itsoff position, an operating circuit for the winding 4520 is from one sideof the line 36 through the knife switch 38, the contact 4|, the segment43, the contact 42, the contacts 2!, 22, and 23, the winding 4611), andthe knife switch 38 to the other side of the line 36. After the relay 46has operated, the portion of the above traced operating circuit throughthe masterswitch 4!: between the contacts 4! and 42 is by-passed by thenow closed contacts 48a through the conductors 5|. It is apparent thatthe relay 46 may be deenergized at any time by the opening of one of thecontacts 2!, 22, and 23.

A plurality of loop circuits 52, 53, and 54 include the operatingwindings 29w, 3520, and 3 lw, respectively, of the annunciator of Fig. 1and also include in series With these windings the plurality ofcondensers 32, 33, and 34, respectively. The loop circuits 52, 53, and54 also include, respectively, the normally-closed contacts 29a, 30a,and 3m of the annunciator as indicated. In the operation of Fig. 2,closure of the knife switch 38 with the master switch 4!! in its offposition and the contacts 2 I, 22, and 23 all closed completes thepreviously traced operating circuit for the winding 46w and the undervoltage relay 46 moves to its operated position. The motor is started bymoving the segment 43' into bridging engagement withthe contacts .44 andwhich completes an obvious energizing circuit for the winding 39wthrough the conductors 5! and the now closed contacts 46a. In responseto energization of its winding 3910, the contactor 39 closes itscontacts 39a and 39b to supply voltage to the motor 35 and theacceleration control means 31 functions in a well-known manner tocontrol the rate of acceleration of the motor 35.

lf any one of the contacts 2|, 22, and 23,

opens, the winding 45w is deenergized and the contacts 416a opentointerrupt the energizing circuit for the winding 39w causing thecontactor 39 to open and the motor 35 to be deenergized. Upon opening ofany of the protective contacts,

the surge voltage produced by the winding 46w causes energization of theannunciator winding connected in parallel with the protective contactthat has opened. This energized annunciator winding functions asdescribed in cpnnectionwith Fig. 1 to provide an indication as to whichprotective contact has opened and also to interrupt the by-pass circuitaround the open protective contact. It is to be noted that thearrangement of the contacts 29a, 30a, and 3| a in Fig. 2 is such thatthe opening of any one of them While its associated protective contactis open positively disconnects the winding 45w from the supply source.The condenser in the loop circuit around the open protective contactalsoserves to insure that no current continues to flowqfrom the line 36to the winding 4611). After one of the protective contacts has opened todropout the relay 4'6, the relay 45 cannot be reclosed to 'permitenergization of the contactor 39 until the master switch 40 has returnedto its off position and all of the protective con-'- tacts are reclosed.Thus, even if the protective contacts reclose upon deenergization of themotor, the motor cannot automatically restart. In any event, a visibleindication as to which protective contact has opened is provided at theannunciator which may be mounted remote from the contacts.

The modification illustrated in Fig. 3 shows the use of a unidirectionalconducting device instead of a condenser in a loop circuit of the typeshown in Figs. 1 and 2. Only the series connected protective contact 2|is shown in Fig. 3 and it is by-passed by a loop circuit 58 including asuitable rectifier 59, the winding 29w of the annunciator, and thenormally-closed contacts 28a connected in series. The rectifier 59 ispreferably of the dry type and has a definite reverse voltage break-downvalue. It is of rugged construction and is so poled with respect to thesupply line I! or 36 that current flow through the winding 2910 isnormally blocked. Upon opening of the contacts 2|, however, thedischarge voltage of the winding I5w or 4610 when added to that of theline voltage is sufiicient to break down the normal blocking action ofthe rectifier 59 and a surge of current passes through the winding 29w.This current is sumcient to operate the annunciator elements associatedwith the winding 2921; and to cause opening of the contacts 29a. Whenthe surge voltage has decreased the normal blocking action of therectifier 59 is restored so that if the contacts 29a should have failedto open, no current can flow through the rectifier 59 to prevent thedrop-out of thecontactor or relay. Since rectifiers currently availablehave a tendency to deteriorate when subjected to excess reverse voltage,this modification is not preferred in those instances in which theannunciator may be called upon to operate frequently.

Fig. 4 illustrates a further modification in which an electronic tube 60is used instead of the condensers of Figs. 1 and 2 and the rectifier ofFig. 3.- The electronic tube 60 is of a well-known type having but twoelectrodes mounted in a gaseous filled envelope and has a predeterminedbreakdown voltage. If the voltage impressed on the electrodes of thetube 60 isbelow the breakdown voltage, the tube 60 conducts nocurrent.However, if the voltage is above the breakdown value, the tube 60conducts current and has but a very low impedance. The breakdown voltageof the tube 60 should be materially above the normal voltage of thesupply lines and materially below the abnormal voltage produced when theline contactor or under-voltage relay is deenergized. The tube 60 thusconstitutes a means responsive to an excess voltage which permitscurrent to flow through the winding 29w upon opening of the contact 2|and which prevents current from flowing in this circuit after theinductive discharge has subsided. It will be understood that otherdevices having suitable operating characteristics may be used instead ofthe condenser, rectifier, and tube. For example, so-called thyrite typeresistors may be used if desired, these having the property ofconducting current only when high voltage is impressed thereon. p Theforegoing description and explanation apply to direct current controlsystems. Ifalternating current is used for the control circuits,reliance cannot be placed for obvious reasons upon the inductive kick ofthe contactor orrelay.

Thecircuits of. Figs. 1 and 2 may, however, be used in alternatingcurrent systems provided that the impedance of the annunciator windingsis large enough to prevent the flow of current of operative magnitude tothe contactor or relay when one of the protective contacts is open. InFig. 1, for example, when the contacts 2i open, the winding 2%; isimmediately energized by current flowing through it and the condenser inseries therewith. Thus operation of the annunciator would be caused bythe voltage normally existing between the lines I! instead of by thesurge voltage as in the case of the direct current system. The winding2911) and the condenser 32, however, must have a low enough impedance topermit the desired current flow to operate the annunciator but must havesuflicient impedance to limit the current through the winding 15w to avalue helow the drop-out value of the contactor 15. This requires a verydelicate balance of impedances. Because of this delicate balance, thecontacts such as 29a, 30a, and am should be included for safety.

Preferably, for alternating current service, the condensers are omittedand external resistors are used instead. As shown in Fig. 5, resistors59 and .10 limit the current that can flow to a winding Hw. of a mainline contactor H for an alternating current motor 72 supplied from asuitable supply line H through a knife switch 75. The 'contactor 'II isprovided with nornially-open auxiliary contacts lid. The motor controlcircuit of Fig. 5 also includes a normally-closed push button 76 and anormally-open push button 18. Only two protective contacts 2| and 22 areshown in Fig. 5 and are by-passed by loop circuits I9 and 80 includingrespectively the resistors E9 and 70, the annunciator windings 29w and36w, and the contacts 29a and 33a.

In the operation of Fig. 5, closure of the ,push button 18 energizes thewinding 'llw by completing a circuit through the contacts 2! and 22 froma single-phase of the supply line 74. Operation of the contactor H inresponse to the energization of its winding 'Hw closes its main contactsto energize the motor 12 and closes its auxiliary contacts Ha tocomplete a holding circuit for the winding 'Hw around the push button 18and through the push button It. Thus the motor 12 may be deenergized atany time after the push button 18 has been released by operation of thepush button '16.

The motor l2is also deenergized when either of the contacts 2! and-'22opens. Upon opening of either one of the protective contacts, thecircuit to the winding 'Hw remains completed for an instant through theloop circuit around the opened contact. Current flowing through the loopcircuit energizes the winding therein and an indication is made of itsenergization. Concurrently, the contacts operated by the annunciatorwinding open and interrupt the only remaining circuit to the windingN20. The contacto-r 1| thereupon drops out to deenergize the motor i2and an indication is left as to which protective contact opened to causethe shut down.

Preferably the impedance .of the loop circuit is .sufiicient to reducethe current in the winding 11w below the drop-out value even though thecontacts 29a or 30a should fail to open. By using these contacts theapplicant assures reasonable safety without the necessity of suchprecise impedance matching.

However, the D.-C. operated control circuit is preferred because of thelarge inductive kick and,

10 when such circuit includes the additional means for interrupting theloop circuits, proper and safe operation of the control without theaccompanying danger of a protective contact being improperly by-passedby the loop circuits is obtained.

Thus the loop circuits around protective contacts can be introduced forindicating while eliminating the hazards normally accompanying the useof such loop circuits.

Instead of employing an annunciator as the indicating device, I may usean operation recorder of known construction or signal lamps which areenergized or deenergized by appropriate relays on the opening of aninterlock contact. The operation recorder has the advantage in that itindicates the nature of the fault, the time of occurrence, and length oftime it existed.

It will be evident that, since the protective contacts, which remainclosed upon the occurrence of a fault, shunt the annunciator coils otherthan the one connected across the protective contact which has opened, afalse indication is impossible. The invention thus has the advantage ofcertainty in operation and indication. In addition, the apparatusinvolved is simple and inexpensive and does not introduce anycomplications into the design or operation of the control circuititself. Since the only moving parts are the annunciator armature andlink,'a minimum of maintenance is required. The annunciator or otherindicating means operates immediately upon the opening of one of theprotective interlocks, and thus no delay is involved in determiningwhich one has opened. The investigation necessary to determine the causeof the existing abnormality may therefore be directed immediately towardthe most likely sources of trouble.

A further advantage of the invention is that the high voltage of theinductive kick is absorbed in sending current through the indicatorcircuit. This prevents burning of the protective contacts upon openingthereof, reduces the voltage stress on the insulation of the conductorsin the main control circuit, and tends to prevent temporary short orsneak circuits which might otherwise result from insulation failure andcause faulty operation of or damage to other current-carrying apparatusconnected to the circuit.

A further advantage of the invention is that,

in event the control bus itself is disconnected automatically inresponse to operation of one of the protective contacts, the inductivekick causes such a rapid and large surge of current that the indicatingmeans is certain to operate either during the short interval requiredfor the contacts in the control bus to open or during the arcinginterval incident to the opening of the control bus contacts. 1

Although I have illustrated and described preferred embodiments of theinvention, it will be recognized that changes in the details ofconstruction and arrangement may be made without departing from thespirit of the invention or the scope of the appended claims.

I claim:

1. A fault indicating system comprising, an electromagnetic devicehaving an operating winding, a supply circuit for said winding, aplurality of normally-closed protective contacts connected in saidsupply circuit and in series with each other and in series with said oneof said contacts, and means respective to said circuits and each beingoperative, after actuation of said indicating means, in response to theflow of current in its associated one of said loop circuits forpreventing the flow of "current, and in its said associated loopcircuit.

each of said last named means including a voltage responsive means inseries with a contact means and in series with the one of said actuatingwindings, in its associated loop circuit, and said contact means beingoperated by its associated one of said actuating windings.

2. A fault indicating system comprising, an

electromagnetic device having an operating winding, a supply circuit forsaid winding, a plurality of normally-closed contacts connected inseries in said supply circuit and in series with said winding, loopcircuits connected around said contacts, respectively, an indicatingmeans having a plurality of actuating windings which are connected insaid loop circuits, respectively, and each of which actuating windingshas an impedance so related to the impedance of said operating windingthat when one of said actuating windings is connected in series withsaid operating winding in said supply circuit said electromagneticdevice remains in a predetermined operated position, and voltageresponsive means in said loop circuits, respectively, each voltageresponsive means being operative to permit a surge of current to flowthrough its assoated loop circuit consequent upon opening of theassociated one of said contacts and thereafter preventing the flow ofcurrent in its loop circuit, the actuating winding in said lastmentioned loop circuit being adapted to become operatively energized bysaid surge to actuate said indicating means.

' 3'. In a fault indicating system, the combination with anelectromagnetic device having an operating winding, a supply circuit forsaid winding, a plurality of normally-closed protective contactsconnected in said supply circuit in series with each other and in serieswith said winding, loop circuits connected around said contacts,respectively, and indicating means having actuating windings connectedin said loop circuits, respectively, and thereby in parallel with thecontacts thereof, and each actuating winding being adapted to becomeoperatively energized, upon opening of the one of said contacts inparallel therewith, to actuate said indicating means, of

two current flow preventing means in each of vent flow of current in theloop circuit containing its said associated actuating winding.

4. A fault indicating system in accordance-with claim 3 characterized inthat one of said current flow preventing means in each loop circuit is acondenser, which by accumulating a charge revents the continued fiow ofcurrent in its associated loop circuit.

1 5. A fault indicating system in accordance with claim 3 characterizedin that one of said current flow preventing means in each loop circuitis a condenser and the other of the current flow preventing means ineach loop circuit is an electromagnetically operated switch contact.

6. In a fault indicating system, the combination with an electromagneticdevice having an operating winding, a supply circuit for said winding, aplurality of normally-closed protective contacts connected in saidsupply circuit in series with each other and in series with saidwinding, loop circuits connected around said contacts, respectively, andindicating means having actuating windings connected in said loopcircuits, respectively, and thereby in parallel with the contactsthereof, and each actuating winding being adapted to become operativelyenergized, upon ings and each, consequent upon opening of its associatedone of said normally-closed contacts and after energization of itsassociated one of said actuating windings and resultant actuation of thesaid indicating means thereby, being operative to prevent the flow ofcurrent in the loop circuit containing its said associated actuatedwinding.

'7. In a fault indicating system, the combination with anelectromagnetic device having an operating winding, a supply circuit forsaid winding, a plurality of normally-closed protective contactsconnected in said supply circuit in series with each other and in serieswith said winding, loop circuits connected around said contacts,respectively, and indicating means having actuat ing windings connectedin said loop circuits, respectively, and thereby in parallel with thecontacts thereof, and each actuating winding being adapted to becomeoperatively energized, upon opening of the one of said contacts inparallel therewith, to actuate said indicating means, of means connectedin said loop circuits, respectively, in series with the actuatingwindings and each, consequent upon opening of its associated one of saidnormally-closed contacts and after energization of its associated one ofsaid actuating windings and resultant actuation of the said indicatingmeans thereby, being operative to prevent the fiow of current in theloop circuit containing its said associated actuated winding, each ofsaid last named means being operative in response to the abnormalvoltage which occurs upon opening of its associated normally-closedcontact.

RUSSELL W. COCHRAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,537,211 Wootton May 12, 19251,901,628 Brainard Mar. 14, 1933 2,127,343 Parlett Aug. 16, 19332,168,805 Pelican Aug. 8, 1939 FOREIGN PATENTS Number Country Date545,982 England June 22, 1942

